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Understanding Model-View-Controller
If I was for example building a calculator application how would I go about splitting functionality so as to follow the MVC design pattern?
Am I right in thinking the following:
View
-Contains all buttons and textfields
Model
-Contains all operations (e.g. add subtract etc)
Controller
Contains all the functions for handling operations and updating display based on user input
Essentially the model acts as a library to the controller in this instance..
If anyone can explain better please do so, but I am struggling to fully grasp the concept..
While you do not technically need to separate an application into MVC, it is more logical to do so. What you have written is essentially correct. The View is your interface to the user. It can be buttons on an iphone or a console on a computer screen. It is independent of the actual function of the application, which is generally in your model, although real basic apps might put some or all functionality in their view controller. A calculator is complicated enough to warrant an independent model class, as you have suggested. The controller is the bridge between the view and the model. So if someone presses a plus button in the view, the controller takes this and sends it to the model.
Related
Thank you for reading this.
These are my first steps in the iPhone Ipad app programming.
In order to learn from scratch (and because I know my app would need dynamic views), I decided not to use Interface Builder.
My question is(regarding the fact that I don't use IB): how would one use Views and Controllers?
I think I understand the MVC concept as it is repeated over and over again in the tutorials I follow, but after the "MVC explanation" part, nothing is made to make it clear "on the field" and closer to the real world (Earth being Xcode here).
Worse, sometimes it seems that some tutorials mix these two concepts up and use one word to say the other.
I read around here a lot of questions (and answers of course) based on the matter but I still don't get it. Sometimes it's too generic, sometimes it's too specific (for me at least).
For what I think I understood, the UIView is the static View when the View Controller is the logic which links the View to the data and those 3 concepts must be separated.
This separation, while a bit clearer with the use of Interface Builder seems to get quite blurry when you code everything as it becomes a virtual soup.
Technically, should I create a specific ".h" and ".m" file for each View AND ALSO for each associated Controller?
If I understand the MVC pattern, it's seems that I should but when I follow tutorials (without IB) it is never the case, view and controllers are created and manipulated within the same implementation files.
Any high level (I'm a noob, don't forget) but still applicable explanation of the use and best practices?
Let's say I want to create a simple app with a green view I can swipe to get to a red view.
I know for sure that I would need at least an:
xxxappDelegate.h
xxxappDelegate.m
xxxView.h
xxxView.m
What else?
1)Where should I put the the second view (along with the first one in "xxxView" or should I create another class h and m file?)?
2) What would the controller(s) do, for that kind of application? In which files would they be created and in which files would they be invoked and how would they "control" the related view?
3) Mainly, regarding to MVC pattern and the fact that there would be no IB, how would you organize that app?
I know it's a lot if you go into the details and code but that's not the point here.
Thank you. This - as simple as it seems - would be of a great help and is not as easily found in tutorials as you might think.
I understand the tutorials I read but they are so particular. As soon as I try to create something on my own which is not a "Hello World" screen, I realize that something is missing, logic wise.
Thank you very much for your help.
Sorry, but I can't get past your first paragraph. If you don't use Interface Builder, you are not going to be a successful iOS programmer. It's that simple. The best advice I've ever read about this is in this Aaron Hillegass interview:
Experienced Cocoa programmers put a lot of the smarts of their application in the NIB file. As a result, their project has a lot less code. Programmers who have spent a few years working in Visual Studio get freaked out. They ask me stuff like, "Can I write Cocoa apps without using Interface Builder? I like to see the code. Maybe I can just explicitly create my windows and the views that go on it?"
It is difficult to explain how the NIB file (and a few other scary ideas) create leverage. It is that leverage that enables one guy in his basement to compete with a team of engineers at Microsoft or Adobe. It is like I showed a chain saw to a early American colonist, and he said, "Can I cut down the tree without starting the engine? I don't like the noise. Maybe I can just bang it against the tree?"
Yes, it's hard to generalize after reading specific tutorials, but you will learn. I thought the learning curve was insurmountable when I first started, but if I can become a programmer that gets paid to write Cocoa software, you can too. Just keep reading and practicing. Don't fight the tools--use them.
Early:
In order to learn from scratch (and because I know my app would need
dynamic views), I decided not to use Interface Builder.
Later:
As soon as I try to create something on my own which is not a "Hello
World" screen, I realize that something is missing, logic wise.
I think what is missing logic wise is that you have accepted your assumption that Interface Builder was a crutch and that to learn "from scratch" you had to avoid using it. You are trying to learn the MVC design pattern but you are not willing to use the tools that have been designed to support it.
In Apple's own documentation they discuss the fact that sometimes there is value in having combined roles—Model Controllers and View Controllers—and that is worth reading, as it may explain some of the code examples you're reviewing. But my primary advice would be: before assuming you know better than the people who built the tools, trying using them the way they recommend. It might be an eye-opener.
Additions later:
OK, so to try and actually answer your questions...
1)Where should I put the the second view (along with the first one in
"xxxView" or should I create another class h and m file?)?
If I am understanding correctly and the two views you are thinking of here are the red and the blue displays to the user, you wouldn't have a second view—what you would do, whether in IB or in code—is to have an element in your view on which you changed a colour property... This would be done programmatically whether you were setting up the parent view in IB or in code.
2) What would the controller(s) do, for that kind of application? In
which files would they be created and in which files would they be
invoked and how would they "control" the related view?
There would be a view controller that would implement the gesture support, and would provide a method for changing the colour of the item in the view between blue and red when that swipe gesture was successfully received. I would have a ViewController.h and and ViewController.m. I think if you were implementing the View entirely in code, it would be implemented in the ViewController.m rather than having a separate View.m. (If you were using IB, you would have a ViewController.h, ViewController.m and ViewController.xib, with the latter providing the basic setup of the view elements and layers.)
You would create a ViewController instance in your AppDelegate.
3) Mainly, regarding to MVC pattern and the fact that there would be
no IB, how would you organize that app?
As above.
If you really insist on going without IB (and I agree 100% with SSteve) then in addition to the files you list you will also want to use a UIViewController. Now, it is important to know that you only need to create header and implementation files when you are adding or changing default behavior.
In you case, the view can probably just be a generic UIView, so you wouldn't need the files. What you would do is subclass UIViewController, and put the swipe logic there. In the swipe logic code you would probably just change the background color of the view.
You would instantiate the view controller in the delegate (in this case anyway) and create the view in the view controller's loadView method. That is required since you won't be using IB.
Personally though, I think that IB does a great job of encouraging proper MVC patterns, and if you are just starting then you should go with IB.
In practice you mostly do not make classes for views, unless they need to do custom drawing or display.
For lightweight configuration of views, that is often done in the viewController's viewDidLoad (or I guess in your case loadView) method.
Yes it's a good idea to keep model and view separated, but that's also balanced with the equally good idea to reduce the amount of code that exists. The less code that is written, the fewer bugs you will have.
Since you are just starting out at this point I would absolutely start by using ARC, and using IB - even though I'm sure you're tired of hearing that from everyone, I'll give you an alternate take. Less code means fewer bugs. And the fact that so many experienced developers are telling you to use it should be a giant clue about what a productive path forward is. I mean, are you doing this to build applications or learn every corner of the UIView class?
To speak to your code example, you do not need the UIView custom class. Just create use a UIViewController's main view as a container view, place a UIView inside with the background set to red. On swipe (using a gesture recognizer attached to the container view) call the UIVew method to swap in a new green-background UIView for the existing red view, you can even define the transition style.
Or create a scroll view in the container view, set up the red and green view inside the scroll view, set the content size and enable paging on the scrollview.
Or create a custom UIView class as you had, listen for touch events and slowly adjust two subview positions to follow the drag action.
Or use an OpenGL backed view, and based on the gesture recognizer pan the scene you are observing with two triangles for a green rectangle and two triangles for a red rectangle.
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I am building a basic app interface which will have a mixture of text, inputfields and buttons. In order to get a working version for project deadline, I thought I would use the default Interface Builder (IB) components for the first iterations and then if there is suffiecient time, I would like to 'jazz up' the interface by adding customised components..
How easy is it to swap over IB components with customised ones at a later stage?
It depends on what you mean exactly by swap over IB components, but in general I would say that IB has full support for customization of your UI within its own conceptual framework. On the other hand, it is pretty obvious that defining your UI programmatically will give you all the customization possibilities you might think of.
In a sense, you can see IB as a way to declare graphically the elements of your UI, their relationships, and have them automatically instantiated for you when the IB xib file is loaded. This is a very flexible mechanism in itself and allows you plenty of possibilities.
Say, for example, that you have a button somewhere in your IB view. In a first release, you could set the class of that button to a plain UIButton; later, you simply specify that that button class is actually a YourCustomClass and you have it, your UI will use your custom button without you having to change much of code (maybe one line or two apart from the custom button implementation). The same holds true for many other kinds of UI elements.
Besides that case, there are classes, like UITableView, that I think are better customizable outside of IB (i.e., by specifying the customization, e.g., the custom cell, programmatically). But still in this case, having the interface defined in IB in the first place is not a big hindrance either, and you simply add the code that you need to your program.
Anyway, there are some customization that are not easily possible with IB. One example could be having more control on how and when your UI components are allocated; so, say, you are restricted to your xib file to be instantiated all at once, while programmatically you could trick every aspect of that. Or, there might be UI elements that are intrisically better suited for a programmatically definition (say, a scrollable grid of pictures), so IB would not fit the bill, or give little support for that (but you would not be able to define that UI elements with it in the first place).
I'm new to iphone development. There's a lot of books on this topic available. But most of the beginner's guides are mostly concerned with Interface Builder usage and lack the information about existing built in XCode code templates or something that could help me in understanding MVC implementation in code. I found that it is possible to write working iOS program without ViewController at all. Well, it seems to me like that after working with the sample code called ViewTransitions.
So, the question is - why is that possible to avoid ViewController implementation in a program that has an interface with a button? If the answer is going to be too long, could you please recommend kind of tutorial or manual covering this topic.
Thanks in advance.
#user697562's answer is essentially correct: in the case of ViewTransitions, the role of the controller is played by the app delegate. The app does next to nothing -- it just switches betweeen two views to demonstrate several possible transition effects -- so a UIViewController isn't really needed there.
Notice that there's also nothing in ViewTransitions that you could really call a model object. If you're looking for a strong example of MVC, ViewTransitions isn't the best project to look at. Other sample projects, such as TheElements, give a better demonstration of MVC in action.
There is a concept called delegation. A concept which helps maintain MVC. It helps to keep the model separate from controllers. For eg: - UITableView/UICollectionView , which knows how to display the data and other ui stuff.
But it does not know which cell to display or what data to display at a particular index. And this is where delegation and the delegate object comes into place. UICollectionView handles all the view part whereas all the non view part is handled by the delgate object, which gives the required data for the view. This way a delegate(usually a separate view controller) acts as a data source and UICollectionView as a ui renderer.
in ViewTransitions, there IS an App Delegate, which is kind of your sole "controller". Even ViewTransitions has:
transition.delegate = self;
IOS is a bit different from some frameworks in that you aren't as "in control" of what is going on. It often uses a delegation model where you set your code as the delegate, but it (IOS) is in control. Still, you can write in MVC style, it's just your "C" isn't fully in charge.
this is a very noobie question although I have had quite a bit of experience iphone development.
I have a client who wants an app with various screnns, but does not want to use built in iphone navigation, but instead wants to have buttons on the screens. All I can find is a load of 14 year olds giving tutorials on MVC or using different views in the same nib.
Does anybody know what apples suggested way of doing this is as I can imagine it been a mind field.
Many thanks
Maybe you should have followed the MVC tutorials of the 14 year old guys.
Then you would know that you could use the built in iphone navigation controllers (ie UITabBarController, UINavigationController) without their standard view counterparts (ie UITabBar, UINavigationBar).
You could always just draw buttons on the screen in interface builder and use custom images for the normal/highlighted states.
When the button is pressed it's up to you what you'd like to do with the received buttonclick method being invoked... the usual way is with the standard navigation system which can optionally have a navigation bar at the top with (back) button, title, etc... and you push/pop viewcontrollers in a hierarchical way. You can just turn the title (or change for your own style) but it does enforce a hierarchical structure.
If you don't want hierarchical navigation of your screens you can either do this with your own custom navigation controller than handles which viewcontroller is currently visible or you could use a thirdparty component like three60 which allows you to navigate around like a webbrowser does on webpages.
You may also want to take a look at Corona which is more for games but would allow you to do a totally custom interface with all sorts of custom transitions and just needs you to write lua... that said it will limit you on using their engine with this approach as you can't get to the ObjC level.
Finally one last approach is simply to use webview and pick up the clicked links so you design your app via webpages... rather ugly approach but can work well if you're very familiar with HTML.
Recently I've been reading up on the MVC pattern and wish to apply it to my iPhone development. However, there seem to be so many variations of the pattern that I'm not sure exactly how it should be applied.
As far as I gather, the view will notify the controller of any actions which have been performed and the controller will in turn update the data model (if required). The data model will notify the view whenever a change to the data occurs and the view then updates it's display of the data appropriately.
In this basic model, the controller only has knowledge of the data model. However, I can't seem to figure out how to employ this design within my iPhone app.
The following page suggests an alternative version of the pattern where the controller has an awareness of both the data model and the view and all communication between the model and view is performed via the controller. It also seems to suggest that the model and view have access to the controller. Would I be right in suggesting that the data model interacts with the controller via some form of notification (notifications or KVO) and that the view interacts with the controller via actions?
Is this second model correct?
http://www.bogotobogo.com/DesignPatterns/mvc_model_view_controller_pattern.html
Many thanks,
Danny
I found Paul Hegartys explanation on MVC in iOS very helpful. see his Stanford iTunes U video. MVC starts at minute 22.
edit
The link of the video doesn't bring you there as expected. it is 1. Introduction to Cocoa Touch, Objective-C, Tools, and MVC (September 21, 2010)
MVC has been around for a long time so there are many variations (or misquotes) to the pattern. Although, the concepts are much the same for most MVC implementations I have seen.
I would focus on how Apple defines MVC. Which can be found in the Cocoa Design Patterns guide and from sample code downloaded from the SDK site (MVCNetworking example).
With iOS you will often will have Models and ViewControllers(which are a merged role of both the controller and the view).
Also, Martin Fowler has some great MVC stuff in his GUI Architectures.
iOS development is very much orientated towards the MVC pattern.
It is usually done with viewControllers and a model. The view is build in Interface Builder, assigned to the controller and the model part is retrieved from elsewhere.
I would say that for Cocoa-Touch the second "version" of the pattern is the one that best describes what usually goes on.
The idea behind MVC is that the model and the view is reusable, but the controller is often fitted to the problem at hand.
This is also true for iOS development, especially if you use interface builder.
The view is hooked up to the viewController via actions/delegates and the model either broadcast its changes through KVO notification or by the controller pulling new data.
There is tons of code available from Apples developer portal and you should start out by looking at some of that code. Having your eyes and mind tuned to looking for the MVC pattern you will see they use it constantly, with the delegate pattern on top to provide event better abstraction
In my opinion, second one is better. Model and view should be separated completely. If view receives notification from model, the view will depends on design of model. By placing controller here, tightly coupled circular-dependency created.
Finally, each part cannot be developed independently, divide-and-conquer strategy is just impossible to use.
My advise for general cases:
Make view and model passive and independent as much as possible. Major mutation must be done with only external manipulation. It should not be changed actively.
Make controller actively controls both of them and other controllers.
In iOS, a UIView is a view which is fully passive. In most cases, all major mutation always done externally by UViewController. And model part should be implemented yourself completely as you want. (Or you can integrate models into controller if it's small enough, however, I don't recommend it)
In some big featured UIView, a sub-scale MVC patterns are used. Fractal!